Radar target simulator

ABSTRACT

Apparatus is disclosed which simulates the operation of a plurality of radar transmitters so as to permit an evaluation of electronic countermeasure equipment. The system generates sequences of pulsed radio frequency signals whose carrier frequency, modulation, amplitude and power lever are controllable to realistically reflect the signal conditions which may be encountered by an aircraft when a multiplicity of radar emitters are operating simultaneously in its vicinity.

nited States Patent Smetana lFelb. 12, 1974 RADAR TARGET SIMULATOR2,928,086 3/1960 Rubino et a1. 343 177 I 3,219,744 11/1965 Mazziotti etal..... 343/17.7 [751 lnvemor- Gary smetana Emwen NY 3,320,349 5/1967Pollack et a1. 343/177 7 Assignee: The United su of America as 2,671,8963/1954 Rosa 343/l7.7

represented by the Secretary of the Navy, Washington, DC. PrimaryExaminer-Maynard R. Wilbur Assistant Examiner-G. E. Montone [22] Flled:1972 Attorney, Agent, or FirmR. S. Sciascia; L. 1. Shrago [21] Appl.No.: 233,065

, [57] ABSTRACT [52] s CL 343/117, 35/104, 343/18 E Apparatus isdisclosed which simulates the operation 51 1111.01 G015 7/40, G06g 7/78of a plurality of radar transmitters so as to Permit [58] Field ofSearch 343/177, 18 E; 35/104; evaluation of electronic countermeasureequipment 325/131, 132, 166, 168 he system generates sequences of pulsedradio frequency signals whose carrier frequency, modulation, [56]Refer'ences Cited amplitude and power lever are controllable torealisti- UNITED STATES PATENTS cally reflect the signal conditionswhich may be encountered by an aircraft when a multiplicity of radar ggzuendorf gig/ emitters are operating simultaneously in its vicinity. rg2,053,780 9/1960 Goldfischer 343/17] 3 Claims, 1 Drawing Figure PRESETI9 1 I COUNTER J PA l T E RN J i I JITTER PULSE J 20 GEN. I 1 GEN. GEN.MOD, 27 1 DRIVER 1 I 10 I 1 14 2 i 1 s- BAND PIN PIN I I osc. 7 2I DIODEDIODE I MOD. I I 3 DRIVER I5 24 I 29 l GAUSSI N M PIN M PIN A 1 ATTEN-gg'gg I 0s 22 010012 01001: I UATER 42 l h, Mon I FREQ. I2\ DRIVER 1 [I6I1 I L METER l X-BAND PIN PIN l I osc. 010015 010012 1 1i 40 41 L HYBRIDg z' JUNCTION DIV|DER "-1 46:1 Js I SBA ND AMP I 44 l 47 STEP I SI 34 I[36 AT8TEN i 1-- C"BAND AMP I ATTEN- H I osc. 1 UATER 49 50 1 l VERNIERI X BAND 5 I ATTEN. I osct AMR I l HIGH POWER SYSTEM TO POWER ECM. METERRADAR TARGET SIMULATOR The present invention relates generally toapparatus for simulating the operation of a multiplicity of radartransmitters and, more particularly, to an arrangement which reproducesthe various signal conditions which may be encountered when amultiplicity of radar sets are operating to detect targets in theirvicinity.

The use of electronic countermeasure systems for jamming or othewiseblocking radar equipment is well known. The effectiveness of thesesystems, to a large extent, depends upon a knowledge of the operationalcharacteristics of the different radars being used. To monitor thiseffectiveness, simulators have been devised to reproduce the radarsignal environment. However, these systems, for the most part, do notrealistically reproduce the actual radar signals because they do nottake into account, for example, any frequency instability orirregularities of the radar transmitters or changing signal conditionsbrought about by different antenna scanning patterns.

The simulator of the present invention permits the evaluation or testingof electronic countermeasure systems under conditions which may involvethe simultaneous processing of a number of signals that duplicate amultiplicity of radar sources having different operationalcharacteristics. The apparatus which accomplishes this includes circuitsfor providing incoherence to the various signals so as to more closelyduplicate the actual operating conditions and to allow the frequencydiscriminating elements of the countermeasure system to be evaluated.Not only are the various signals given an arbitrary degree of frequencyinstability but, additionally, the number of signals in any one periodof time may be controlled to ascertain how the system responds to alimited exposure to the various radar transmitters. To further improvethe realistic nature of the radar signal environment, all of the radiofrequency signals may have their modulation controlled to conform todifferent selected antenna scanning patterns. Furthermore, the amplitudeof the signals may be changed over wide limits to check, for example,the priority of decision-making ability of the countermeasure systemunder test. Thus, a weak but imminent radar threat can be simulated in afrequency adjacent to a strong but nonthreat radar signal, allowingdetection and proper response to the threat signal.

It is accordingly a primary object of the present invention to provide asystem for simulating an environment wherein a nultiplicity of radarsignals are present in order to evaluate the response of electroniccountermeasure systems.

Another object of the present invention is to provide a simulator whichdevelops a multiplicity of radio frequency signals having diversecharacteristics which closely reflect signal conditions which occur inan area under radar surveillance.

Another object of the present invention is to provide a simulator foruse in evaluating electronic countermeasure equipment to determine itseffectiveness in classifying various radar transmitters.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawing, the singleFIGURE of which schematically illustrates the one illustrativeembodiment of the invention.

Referring now to this FIGURE, it will be seen that the over-allsimulator at one end is'subdivided into a lowpower signal processingsystem and a high-power system which differ only to the extent thatappropriate high-power amplifying circuits are included in the lattersystem in order to develop corresponding signals of greater amplitude.

The low-power system includes an S-band oscillator 10, a C-bandoscillator 11 and an X-band oscillator 12, with each adapted to have itsfrequency varied by a common Gaussian noise source 13. Each of theoscillators thus develops a continuous output signal whose frequency atany one particular time departs from its center or average value by anamount depending upon the amplitude of the signal then being supplied toits control circuit from noise source 13. Since this source is of arandom nature, a similar degree of randomness is imparted to the outputsignals from the various oscillators.

It will be appreciated that this method of controlling the variousoscillators provides incoherence to each of the signal sources in theover-all system and creates a frequency instability which reproduces toa high degree an actual radar environment.

To form pulsed radio frequency signals, the outputs of the oscillatorsare supplied to PIN diodes 14, 15 and 16. Each of these diodes isadapted to be biased to conduction by a pulse derived from pulsegenerator 17. This pulse generator, therefore, has its output fed tosuitable modulator drivers 20, 21 and 22 which are in the controlcircuits of these diode assemblies. These drivers, it will beappreciated, merely impart to the pulse appropriate powercharacteristics for controlling the individual diodes.

In order to better simulate actual operating conditions, the periodbetween successive pulses generated by pulse generator 17 is notmaintained constant but is subjected to a certain amount of variation bya socalled jitter generator 18. This generator is coupled to pulsegenerator 17 in a manner which allows it to control the synchronizationof the generator and produce pulses whose interpulse spacing contains acertain amount of randomness.

Although the jitter generator 18 is shown as a single signal source, itwould be pointed out that in actual practice this apparatus may consistof, for example, a first free-running oscillator whose frequency may beswitch-selectable at increments of 10, 10.1, 10.2, 10.5 and l 1.0 Hz anda second free-running oscillator, also switch-selectable, at l, 2, 5 and10 KHZ. These two signals are superimposed such that only particularcombinations of voltage and time will fire the basic oscillator. The lowfrequency selection thus defines the amount of dispersion or jitterabout the basic oscillator frequency. With the above selectionavailable, a randomly varying l, 2, 5 or 10 KHz signal may be producedwith 1, 2, 5 or 10 percent dispersion.

Pulse generator 17 is also under the control of a counter 19 coupledthereto in a closed loop circuit which regulates the number of pulsesbeing produced. Thus, if the apparatus under test is to be evaluatedwith only a predetermined number of input signals, this number can beestablished by the setting of counter 19 and, once this number of pulseshas been produced, this phase of the simulator system will be inactiveuntil reset.

The outputs of the various diodes l4, l5, 16 are thus a predeterminednumber of pulsed RF signals at the S, C and X-band frequency, allpossessing a certain amount of frequency instability due to noise source13 and having a random interpulse spacing as determined by generator 18.Thus, instead of modulating the radio frequency carrier with, forexample, a stable 1 KHz frequency, the action of jitter generator 18permits modulation at this frequency but with selectable amounts offrequency instability, for example, i, 2, 5 or percent. As a result ofthis instability, the system better reflects actual operatingconditions.

The output of diodes 14, 15, 16 are supplied to a second group of PINdiodes 23, 24 and 25. These diodes are biased to conduction by anantenna scan pattern generator 26 which can be selectively coupled tothese different diodes through switch 27. The signal derived fromgenerator 26 has a wave form which is calculated to impart to the inputsignals an amplitude envelope corresponding to that encountered in anactual operating environment where the radar signal, for example, isbeing spatially revolved in a particular antenna scanning (groundsearch) mode.

It will be appreciated that although only one pattern generator is shownconnected to switch 27, a multiplicity of generators may be used witheach having a particular wave form corresponding to the radar signalassociated with a different antenna scanning configuration. In the casewhere the apparatus is intended to simulate a ground search radar, thescan pattern generator produces an amplitude envelope signal whichcontains a major lobe peak having appropriate first and second side-lobeminor peaks symmetrically positioned on opposite sides thereof. Thissignal is superimposed upon the modulated radio frequency signal suchthat the pulsing radio frequency signal amplitude changes with time andis not constant. This feature is significant, as mentioned previously,in that it allows a real-world checkout of the countermeasure systemsprocessing capability on minimum and/or changing amplitude emitter data.The decision-making mode of the system can therefore be evaluated, thatis, should the aircraft's pilot be directed to ignore, evade or destroythe radar emitter.

The high power portion of the over-all system likewise contains anS-band, C-band and X-band oscillator, elements 30, 31 and 32, whosefrequencies are also adapted to be varied by a noise source, not shown,so as to duplicate the performance of the signal sources in the lowpower system. However, the output of the individual oscillators aresubjected to amplification in amplifiers 33, 34 and 35 before beingapplied to the diodes which modulate these carrier waves to produce thedesired pulsed signals. The purpose of generating the high power signalsis to permit saturation testing of the receivers that are part of theelectronic countermeasure equipment.

Each power system thus has three different output lines, correspondingto a different frequency band, and a switching device, such as 28 in thelow power system, is provided to selectively couple any one of theselines to an attenuator 29 or 36 feeding a hybrid junction 40. By meansof this arrangement, for example, two signals of the same frequency canbe extracted which have different modulation parameters or amplitudelevels, representing either one or two completely independent radartargets. Likewise, two distinctly different signals may be formed atdifferent frequencies with different modulation characteristics topermit a check of the priority decision-making capability of theapparatus under test.

The hybrid junction 40 multiplexes the two signals fed thereto fromattenuators 29 and 36, and the output of this junction is coupled to afour-way power divider 41 which, in effect, channels these signals intofour different lines in which these signals are available for furtherindependent signal processing. Connected to the power divider by meansof a suitable output port is a frequency meter 42 for initial targetset-up purposes on the desired frequency or frequencies.

The four output lines 43, 44, 45, 46 contain independently controlled,precision step attenuators, such as 47, and, thereafter, a suitablearray of coaxial switches, such as 48, for further subdividing theselines into a greater number of branches. Each of these branches includesvernier attenuators, such as 49 and 50, which can modify the signallevel in a manner which gives the appearance of a signal source that is,in effect, moving into a different apparent spatial location withrespect to the electronic countermeasure equipment. After thisattenuation, all of the branch lines may be directly connected viasuitable connectors to what corresponds to the antenna input ports ofthe electronic countermeasure receivers. Because of this directconnection, an RF power algorithm is established which relates powermeasurement to an apparent spatial location with respect to theboresight of, for example, any aircraft which might be carryingelectronic countermeasure equipment similar to that under test. For thispurpose, each of the branch lines contains suitable switching apparatusfor selectively feeding the signal appearing in that line to a digitalmicrowave power meter, such as 51. The independently-controllable (inamplitude) eight lines can be set up such that the lines that are theforward-looking antenna inputs are set to a maximum signal level, andthe other six lines set at relatively smaller signal levels, thuscreating a spatial location of a signal coming at the front of theaircraft, or the rear, or the side, as desired.

For simplicitys sake, only one output line from power divider 41 isshown with its various attenuators and complementary switching devices.However, each of the output lines is so constructed to yield eightpossible output connections with four adapted to be directly wired tothe input of the countermeasure receiver and four adapted to be coupledto power meters, such as 51.

What is claimed is:

1. Apparatus for simulating the operation of a plurality of radartransmitters comprising, in combination,

an S-band, C-band and X-band oscillator,

each of said oscillators being controlled by a Gaussian noise sourcesuch that the output signal of these oscillators varies in frequency ina random manner about a median value;

a pulse generator for producing a sequence of pulses,

said pulse generator being controlled such that the time intervalbetween adjacent pulses of said sequence is irregular;

means for modulating the output signals from said oscillators such thatradio frequency pulses are produced corresponding in time and durationto said pulses;

means for controlling the relative amplitude of said radio frequencypulses so as to develop a sequence of radio frequency pulses whichcorresponds to the radio frequency pulses radiated in a particulardirection by a radar transmitter that is operating in a particularscanning mode; and means for selectively connecting a particularsequence of amplitude modulated radio frequency pulses to an outputcircuit so as to have them available thereat for testing the performanceof electromagnetic countermeasure equipment. 2. Apparatus for simulatingthe performance of a plurality of radar transmitters which are operatingin a particular scanning mode comprising, in combination,

an S-band, C-band and X-band oscillator,

each of said oscillators being under the control of a Gaussian noisesource such that the output signal of each oscillator is a continuoussignal whose frequency randomly varies about a median value; means forcoupling the output signal of each oscillator to one input of a PINdiode; means for generating a first sequence of pulses whose interpulsespacings show a jitter effect such that these pulses occur at irregulartime intervals; means for feeding said sequence of pulses to the controlelectrode of each-PIN diode whereby corresponding radio frequency pulsesat said S, C and X-bands appear in the output circuit of each PIN diode;

means for controlling the amplitude of said radio frequency pulses suchthat each sequence of radio frequency pulses correspond to the radiofrequency pulses that are radiated in a particular direction by a radarset whose antenna has a particular scanning pattern;

a network of signal attenuating means; and

means for coupling one of said particular pulse sequences to saidnetwork whereby said particular pulse sequence may be subjected tovariable amounts of attenuation before being coupled to the electroniccountermeasure equipment that is to be tested.

3. In an arrangement as defined in claim 2,

means for producing a sequence of amplified radio frequency pulses atsaid S, C and X-bands, said amplified radio frequency pulses also havingirregular time intervals between pulses;

means for controlling the relative amplitudes of said amplified radiofrequency pulses so as to have these pulses correspond to the radiofrequency pulses that are radiated in a particular direction by a radarset whose antenna has a particular scanning pattern; and

means for selectively coupling said amplified pulse sequence to saidnetwork of signal attenuating means.

2. Apparatus for simulating the performance of a plurality of radartransmitters which are operating in a particular scanning modecomprising, in combination, an S-band, C-band and X-band oscillator,each of said oscillators being under the control of a Gaussian noisesource such that the output signal of each oscillator is a continuoussignal whose frequency randomly varies about a median value; means forcoupling the output signal of each oscillator to one input of a PINdiode; means for generating a first sequence of pulses whose interpulsespacings show a jitter effect such that these pulses occur at irregulartime intervals; means for feeding said sequence of pulses to the controlelectrode of each PIN diode whereby corresponding radio frequency pulsesat said S, C and X-bands appear in the output circuit of each PIN diode;means for controlling the amplitude of said radio frequency pulses suchthat each sequence of radio frequency pulses correspond to the radiofrequency pulses that are radiated in a particular direction by a radarset whose antenna has a particular scanning pattern; a network of signalattenuating means; and means for coupling one of said particular pulsesequences to said network whereby said particular pulse sequence may besubjected to variable amounts of attenuation before being coupled to theelectronic countermeasure equipment that is to be tested.
 3. In anarrangement as defined in claim 2, means for producing a sequence ofamplified radio frequency pulses at said S, C and X-bands, saidamplified radio frequency pulses also having irregular time intervalsbetween pulses; means for controlling the relative amplitudes of saidamplified radio frequency pulses so as to have these pulses correspondto the radio frequency pulses that are radiated in a particulardirection by a radar set whose antenna has a particular scanningpattern; and means for selectively coupling said amplified pulsesequence to said network of signal attenuating means.